add license header to files; update readme disclaimer

[noot]

related to #326

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.06 :warning:

Comparison is base (aa70b55) 54.29% compared to head (f7ae4c8) 54.24%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #368 +/- ## ========================================== - Coverage 54.29% 54.24% -0.06% ========================================== Files 93 93 Lines 7967 7967 ========================================== - Hits 4326 4322 -4 - Misses 3097 3101 +4 Partials 544 544 ``` | [Impacted Files](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [cliutil/utils.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y2xpdXRpbC91dGlscy5nbw==) | `55.55% <ø> (ø)` | | | [cmd/swapd/contract.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y21kL3N3YXBkL2NvbnRyYWN0Lmdv) | `73.21% <ø> (ø)` | | | [cmd/swapd/main.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y21kL3N3YXBkL21haW4uZ28=) | `70.09% <ø> (ø)` | | | [cmd/swapd/profile.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y21kL3N3YXBkL3Byb2ZpbGUuZ28=) | `15.15% <ø> (ø)` | | | [cmd/swapd/signal\_handler.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y21kL3N3YXBkL3NpZ25hbF9oYW5kbGVyLmdv) | `0.00% <ø> (ø)` | | | [coins/coins.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y29pbnMvY29pbnMuZ28=) | `85.61% <ø> (ø)` | | | [coins/common.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y29pbnMvY29tbW9uLmdv) | `100.00% <ø> (ø)` | | | [coins/exchange\_rate.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y29pbnMvZXhjaGFuZ2VfcmF0ZS5nbw==) | `72.72% <ø> (ø)` | | | [coins/exponent.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y29pbnMvZXhwb25lbnQuZ28=) | `100.00% <ø> (ø)` | | | [coins/provides.go](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y29pbnMvcHJvdmlkZXMuZ28=) | `85.00% <ø> (ø)` | | | ... and [80 more](https://codecov.io/gh/AthanorLabs/atomic-swap/pull/368?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None)

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[noot]

@dimalinux from what I understand, LGPL code can be used in other applications as a library without needing to reveal the source code as long as the library code has not been modified. in the case where the code has been modified from the source, the application would need to release that modified LGPL code, and in the case of static linking then they'd need to release the entire app's source. so there is nothing preventing a project that isn't (L)GPL from using this code unmodified. if there is ever a case where the license seriously becomes an issue, I'm happy to discuss it further.

we could also look into adding the static linking exception.

edit: apparently go-ethereum is LGPL https://github.com/ethereum/go-ethereum